Epicyclic gear train

ABSTRACT

A turbine engine according to an example of the present disclosure includes, among other things, a fan shaft, at least one tapered bearing mounted on the fan shaft, the fan shaft including at least one passage extending in a direction having at least a radial component, and adjacent the at least one tapered bearing, a fan mounted for rotation on the at least one tapered bearing. An epicyclic gear train is coupled to drive the fan, the epicyclic gear train including a carrier supporting intermediate gears that mesh with a sun gear, and a ring gear surrounding and meshing with the intermediate gears, wherein the epicyclic gear train defines a gear reduction ratio of greater than or equal to 2.3. A turbine section is coupled to drive the fan through the epicyclic gear train, the turbine section having a fan drive turbine that includes a pressure ratio that is greater than 5. The fan includes a pressure ratio that is less than 1.45, and the fan has a bypass ratio of greater than ten (10).

CROSS REFERENCE TO RELATED APPLICATIONS

The present disclosure is a continuation of U.S. patent application Ser.No. 14/824,351, filed Aug. 12, 2015, which is a continuation-in-part ofU.S. patent application Ser. No. 13/486,766, filed Jun. 1, 2012, whichis a continuation of U.S. patent application Ser. No. 13/340,735, filedDec. 30, 2011, now U.S. Pat. No. 8,708,863, granted Apr. 29, 2014, whichis a continuation-in-part of U.S. patent application Ser. No.11/504,220, filed Aug. 15, 2006, now U.S. Pat. No. 8,753,243, grantedJun. 17, 2014.

BACKGROUND OF THE INVENTION

This invention relates to a ring gear used in an epicyclic gear train ofa gas turbine engine.

Gas turbine engines typically employ an epicyclic gear train connectedto the turbine section of the engine, which is used to drive the turbofan. In a typical epicyclic gear train, a sun gear receives rotationalinput from a turbine shaft through a compressor shaft. A carriersupports intermediate gears that surround and mesh with the sun gear. Aring gear surrounds and meshes with the intermediate gears. Inarrangements in which the carrier is fixed against rotation, theintermediate gears are referred to as “star” gears and the ring gear iscoupled to an output shaft that supports the turbo fan.

Typically, the ring gear is connected to the turbo fan shaft using aspline ring. The spline ring is secured to a flange of the turbo fanshaft using circumferentially arranged bolts. The spline ring includessplines opposite the flange that supports a splined outercircumferential surface of the ring gear. The ring gear typicallyincludes first and second portions that provide teeth facing in oppositedirections, which mesh with complimentary oppositely facing teeth of thestar gears.

An epicyclic gear train must share the load between the gears within thesystem. As a result, the splined connection between the ring gear andspline ring is subject to wear under high loads and deflection. Sincethe spline connection requires radial clearance, it is difficult to geta repeatable balance of the turbo fan assembly. Balance can alsodeteriorate over time with spline wear.

SUMMARY OF THE INVENTION

In a featured embodiment, a turbine engine has a fan shaft. At least onetapered bearing is mounted on the fan shaft. The fan shaft includes atleast one passage extending in a direction having at least a radialcomponent, and adjacent the at least one tapered bearing. A fan ismounted for rotation on the tapered bearing. An epicyclic gear train iscoupled to drive the fan. The epicyclic gear train includes a carriersupporting intermediate gears that mesh with a sun gear. A ring gearsurrounds and meshes with the intermediate gears. Each of theintermediate gears are supported on a respective journal bearing. Theepicyclic gear train defines a gear reduction ratio of greater than orequal to about 2.3. A turbine section is coupled to drive the fanthrough the epicyclic gear train. The turbine section has a fan driveturbine that includes a pressure ratio that is greater than about 5. Thefan includes a pressure ratio that is less than about 1.45, and the fanhas a bypass ratio of greater than about ten (10).

In another embodiment according to the previous embodiment, the fanshaft is coupled to the ring gear.

In another embodiment according to any of the previous embodiments, theat least one tapered bearing includes a first tapered bearing and the atleast one passage includes a first passage and a second passage. Thefirst passage is located at an axially forward side of the first taperedbearing and the second passage is located at an axially aft side of thefirst tapered bearing.

In another embodiment according to any of the previous embodiments, thefan shaft includes, on a radially inner surface, at least one wellextending between axial sides and a radial side, and the at least onepassage opens at the radial side.

In another embodiment according to any of the previous embodiments, thefan shaft includes, on a radially inner surface, a plurality of wellseach extending between axial side walls and a radial side wall, and theat least one passage includes a plurality of passages that open atrespective ones of the radial side walls of the plurality of wells.

In another embodiment according to any of the previous embodiments, twowells of the plurality of wells are axially adjacent such that the twowells share a common axial side wall.

In another embodiment according to any of the previous embodiments, theaxial side walls are gradually sloped.

In another embodiment according to any of the previous embodiments, theepicyclic gear train has a gear reduction ratio of greater than or equalto 2.3.

In another embodiment according to any of the previous embodiments, theepicyclic gear train has a gear reduction ratio of greater than or equalto about 2.5.

In another embodiment according to any of the previous embodiments, theepicyclic gear train has a gear reduction ratio of greater than or equalto 2.5.

In another embodiment according to any of the previous embodiments, thefan defines a bypass ratio of greater than about 10.5:1 with regard to abypass airflow and a core airflow.

In another embodiment according to any of the previous embodiments,there are three turbines, with the fan drive turbine being a lowestpressure turbine, and there being a high pressure turbine and anintermediate pressure turbine, with the high pressure turbine and theintermediate pressure turbine each driving a compressor rotor.

Although different examples have the specific components shown in theillustrations, embodiments of this invention are not limited to thoseparticular combinations. It is possible to use some of the components orfeatures from one of the examples in combination with features orcomponents of another of the examples.

These and other features disclosed herein can be best understood fromthe following specification and drawings, the following of which is abrief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-sectional view of a front portion of a gasturbine engine illustrating a turbo fan, epicyclic gear train and acompressor section.

FIG. 2 is an enlarged cross-sectional view of the epicyclic gear trainshown in FIG. 1.

FIG. 3 is an enlarged cross-sectional view of an example ring gearsimilar to the arrangement shown in FIG. 2.

FIG. 4 is a view of the ring gear shown in FIG. 3 viewed in a directionthat faces the teeth of the ring gear in FIG. 3.

FIG. 5 shows another embodiment.

FIG. 6 shows yet another embodiment.

DETAILED DESCRIPTION

A portion of a gas turbine engine 10 is shown schematically in FIG. 1.The turbine engine 10 includes a fixed housing 12 that is constructedfrom numerous pieces secured to one another. A compressor section 14having compressor hubs 16 with blades are driven by a turbine shaft 25about an axis A. A turbo fan 18 is supported on a turbo fan shaft 20that is driven by a compressor shaft 24, which supports the compressorhubs 16, through an epicyclic gear train 22.

In the example arrangement shown, the epicyclic gear train 22 is a stargear train. Referring to FIG. 2, the epicyclic gear train 22 includes asun gear 30 that is connected to the compressor shaft 24, which providesrotational input, by a splined connection. A carrier 26 is fixed to thehousing 12 by a torque frame 28 using fingers (not shown) known in theart. The carrier 26 supports star gears 32 using journal bearings 34that are coupled to the sun gear 30 by meshed interfaces between theteeth of sun and star gears 30, 32. Multiple star gears 32 are arrangedcircumferentially about the sun gear 30. Retainers 36 retain the journalbearings 34 to the carrier 26. A ring gear 38 surrounds the carrier 26and is coupled to the star gears 32 by meshed interfaces. The ring gear38, which provides rotational output, is secured to the turbo fan shaft20 by circumferentially arranged fastening elements, which are describedin more detail below.

As shown, each of the star gears 32 is supported on one of the journalbearings 34. Each journal bearing 34 has an internal central cavity 34 athat extends between axial ends 35 a and 35 b. In this example, asshown, the internal central cavity 34 a is axially blind in that theaxial end 35 a is closed. At least one passage 37 extends from theinternal central cavity 34 a to a peripheral journal surface 39. In theexample, the at least one passage 37 includes a first passage 37 a and asecond passage 37 b that is axially spaced form the first passage 37 a.As shown, the first and second passages 37 a and 37 a are non-uniformlyspaced with regard to the axial ends 35 a and 35 b of the internalcentral cavity 34 a.

In operation, lubricant is provided to the internal central cavity 34 a.The lubricant flows through the internal central cavity 34 a and thenoutwardly through the at least one passage 37 to the peripheral journalsurface 39. The arrangement of the internal central cavity 34 a and atleast one passage 37 thereby serves to cool and lubricate the journalbearing 32.

The gas turbine engine 10 is a high-bypass geared architecture aircraftengine. In one disclosed, non-limiting embodiment, the engine 10 has abypass ratio that is greater than about six (6) to ten (10), theepicyclic gear train 22 is a planetary gear system or other gear systemwith a gear reduction ratio of greater than about 2.3 or greater thanabout 2.5, and a low pressure turbine of the engine 10 has a pressureratio that is greater than about 5. In one disclosed embodiment, theengine 10 bypass ratio is greater than about ten (10:1) or greater thanabout 10.5:1, the turbofan 18 diameter is significantly larger than thatof the low pressure compressor of the compressor section 14, and the lowpressure turbine has a pressure ratio that is greater than about 5:1. Inone example, the epicyclic gear train 22 has a gear reduction ratio ofgreater than about 2.3:1 or greater than about 2.5:1. It should beunderstood, however, that the above parameters are only exemplary of oneembodiment of a geared architecture engine and that the presentinvention is applicable to other gas turbine engines including directdrive turbofans.

A significant amount of thrust is provided by a bypass flow B due to thehigh bypass ratio. The fan 18 of the engine 10 is designed for aparticular flight condition—typically cruise at about 0.8 M and about35,000 feet. The flight condition of 0.8 M and 35,000 ft, with theengine at its best fuel consumption—also known as “bucket cruiseTSFC”—is the industry standard parameter of lbm of fuel being burneddivided by lbf of thrust the engine produces at that minimum point. “Lowfan pressure ratio” is the pressure ratio across the fan blade alone.The low fan pressure ratio as disclosed herein according to onenon-limiting embodiment is less than about 1.45. “Low corrected fan tipspeed” is the actual fan tip speed in ft/sec divided by an industrystandard temperature correction of [(Tambient deg R)/518.7)̂0.5]. The“Low corrected fan tip speed” as disclosed herein according to onenon-limiting embodiment is less than about 1150 ft/second.

Referring to FIGS. 3 and 4, the ring gear 38 is a two-piece constructionhaving first and second portions 40, 42. The first and second portions40, 42 abut one another at a radial interface 45. A trough 41 separatesoppositely angled teeth 43 (best shown in FIG. 4) on each of the firstand second portions 40, 42. The arrangement of teeth 43 forces the firstand second portions 40, 42 toward one another at the radial interface45. The back side of the first and second portions 40, 42 includes agenerally S-shaped outer circumferential surface 47 that, coupled with achange in thickness, provides structural rigidity and resistance tooverturning moments. The first and second portions 40, 42 have a firstthickness T1 that is less than a second thickness T2 arranged axiallyinwardly from the first thickness T1. The first and second portions 40,42 include facing recesses 44 that form an internal annular cavity 46.

The first and second portions 40, 42 include flanges 51 that extendradially outward away from the teeth 43. The turbo fan shaft 20 includesa radially outwardly extending flange 70 that is secured to the flanges51 by circumferentially arranged bolts 52 and nuts 54, which axiallyconstrain and affix the turbo fan shaft 20 and ring gear 38 relative toone another. Thus, the spline ring is eliminated, which also reducesheat generated from windage and churning that resulted from the sharpedges and surface area of the splines. The turbo fan shaft 20 and ringgear 38 can be rotationally balanced with one another since radialmovement resulting from the use of splines is eliminated. An oil baffle68 is also secured to the flanges 51, 70 and balanced with the assembly.

Seals 56 having knife edges 58 are secured to the flanges 51, 70. Thefirst and second portions 40, 42 have grooves 48 at the radial interface45 that form a hole 50, which expels oil through the ring gear 38 to agutter 60 that is secured to the carrier 26 with fasteners 61 (FIG. 2).The direct radial flow path provided by the grooves 48 reduces windageand churning by avoiding the axial flow path change that existed withsplines. That is, the oil had to flow radially and then axially to exitthrough the spline interface. The gutter 60 is constructed from a softmaterial such as aluminum so that the knife edges 58, which areconstructed from steel, can cut into the aluminum if they interfere.Referring to FIG. 3, the seals 56 also include oil return passages 62provided by first and second slots 64 in the seals 56, which permit oilon either side of the ring gear 38 to drain into the gutter 60. In theexample shown in FIG. 2, the first and second slots 64, 66 are insteadprovided in the flange 70 and oil baffle 68, respectively.

FIG. 5 shows an embodiment 200, wherein there is a fan drive turbine 208driving a shaft 206 to in turn drive a fan rotor 202. A gear reduction204 may be positioned between the fan drive turbine 208 and the fanrotor 202. This gear reduction 204 may be structured and operate likethe gear reduction disclosed above. A compressor rotor 210 is driven byan intermediate pressure turbine 212, and a second stage compressorrotor 214 is driven by a turbine rotor 216. A combustion section 218 ispositioned intermediate the compressor rotor 214 and the turbine section216.

FIG. 6 shows yet another embodiment 300 wherein a fan rotor 302 and afirst stage compressor 304 rotate at a common speed. The gear reduction306 (which may be structured as disclosed above) is intermediate thecompressor rotor 304 and a shaft 308 which is driven by a low pressureturbine section.

Although embodiments of this invention have been disclosed, a worker ofordinary skill in this art would recognize that certain modificationswould come within the scope of this invention. For that reason, thefollowing claims should be studied to determine the true scope andcontent of this invention.

What is claimed is:
 1. A turbine engine comprising: a fan shaft; atleast one tapered bearing mounted on the fan shaft, the fan shaftincluding at least one passage extending in a direction having at leasta radial component, and adjacent the at least one tapered bearing; a fanmounted for rotation on the at least one tapered bearing; an epicyclicgear train coupled to drive the fan, the epicyclic gear train includinga carrier supporting intermediate gears that mesh with a sun gear, and aring gear surrounding and meshing with the intermediate gears, whereinthe epicyclic gear train defines a gear reduction ratio of greater thanor equal to 2.3; and a turbine section coupled to drive the fan throughthe epicyclic gear train, the turbine section having a fan drive turbinethat includes a pressure ratio that is greater than 5, the fan includesa pressure ratio that is less than 1.45, and the fan has a bypass ratioof greater than ten (10).
 2. The turbine engine as recited in claim 1,wherein the fan is supported on the fan shaft.
 3. The turbine engine asrecited in claim 2, wherein the at least one tapered bearing includes afirst tapered bearing, and the at least one passage includes a firstpassage and a second passage.
 4. The turbine engine as recited in claim3, wherein the first passage is located at an axially forward side ofthe first tapered bearing, and the second passage is located at anaxially aft side of the first tapered bearing.
 5. The turbine engine asrecited in claim 2, wherein the fan shaft includes, on a radially innersurface, at least one well extending between axial sides and a radialside, and the at least one passage opens at the radial side.
 6. Theturbine engine as recited in claim 5, wherein the at least one well is aplurality of wells each extending between axial side walls and a radialside wall, and the at least one passage includes a plurality of passagesthat open at respective ones of the radial side walls of the pluralityof wells.
 7. The turbine engine as recited in claim 6, wherein two wellsof the plurality of wells are axially adjacent such that the two wellsshare a common axial side wall.
 8. The turbine engine as recited inclaim 7, wherein the axial side walls are gradually sloped.
 9. Theturbine engine as recited in claim 7, wherein the epicyclic gear trainhas a gear reduction ratio of greater than or equal to 2.5.
 10. Theturbine engine as recited in claim 9, wherein the fan defines a bypassratio of greater than 10.5:1 with regard to a bypass airflow and a coreairflow, and a low corrected fan tip speed of less than 1150 ft/second.11. The turbine engine as recited in claim 10, wherein the epicyclicgear train is intermediate a compressor rotor and a shaft driven by thefan drive turbine such that a fan rotor and a first stage compressor arerotatable at a common speed.
 12. The turbine engine as recited in claim2, wherein the ring gear includes a first portion and a second portionthat abuts the first portion at a radial interface.
 13. The turbineengine as recited in claim 12, wherein a trough separates oppositelyangled teeth on each of the first and second portions.
 14. The turbineengine as recited in claim 13, wherein the first and second portionsinclude respective flanges that extend radially outward away from theteeth.
 15. The turbine engine as recited in claim 14, wherein each ofthe intermediate gears is supported on a respective journal bearing. 16.The turbine engine as recited in claim 15, wherein the first and secondportions have grooves at the radial interface that form a hole thatexpels oil through the ring gear to a gutter that is secured to thecarrier.
 17. The turbine engine as recited in claim 16, wherein abackside of the respective first and second portions includes agenerally S-shaped outer circumferential surface.
 18. The turbine engineas recited in claim 16, wherein the fan shaft is coupled to the ringgear.
 19. The turbine engine as recited in claim 18, wherein the fanshaft includes a radially outward extending flange secured to theflanges of the first and second portions.
 20. The turbine engine asrecited in claim 19, wherein the epicyclic gear train has a gearreduction ratio of greater than or equal to 2.5, the fan defines abypass ratio of greater than 10.5:1, and a low corrected fan tip speedof less than 1150 ft/second.
 21. The turbine engine as recited in claim20, wherein the sun gear is connected to a compressor shaft by a splinedconnection.
 22. The turbine engine as recited in claim 12, wherein theat least one tapered bearing includes a first tapered bearing, the atleast one passage is a plurality of passages including a first passageand a second passage, the first passage is located at an axially forwardside of the first tapered bearing, and the second passage is located atan axially aft side of the first tapered bearing.
 23. The turbine engineas recited in claim 22, wherein the fan shaft includes, on a radiallyinner surface, a plurality of wells each extending between axial sidewalls and a radial side wall, and the plurality of passages open atrespective ones of the radial side walls of the plurality of wells. 24.The turbine engine as recited in claim 23, wherein two wells of theplurality of wells are axially adjacent such that the two wells share acommon axial side wall.
 25. The turbine engine as recited in claim 24,wherein the first and second portions include respective flanges thatextend radially outward away from the teeth.
 26. The turbine engine asrecited in claim 25, wherein the first and second portions have groovesat the radial interface that form a hole that expels oil duringoperation through the ring gear to a gutter that is secured to thecarrier, and the first and second portions include facing recesses thatform an internal annular cavity.
 27. The turbine engine as recited inclaim 26, further comprising: seals having knife edges secured to theflanges of the first and second portions; and wherein the seals includeoil return passages provided by slots in the seals, or provided in aradially outward extending flange of the fan shaft and an oil bafflesecured to the carrier, the radially outward extending flange secured tothe flanges of the first and second portions.
 28. The turbine engine asrecited in claim 27, wherein each of the intermediate gears is supportedon a respective journal bearing, each journal bearing has an internalcentral cavity that extends between axial ends, and at least one passagethat extends from the internal central cavity to a peripheral journalsurface of the respective journal bearing.
 29. The turbine engine asrecited in claim 28, wherein the epicyclic gear train has a gearreduction ratio of greater than or equal to 2.5, the fan defines abypass ratio of greater than 10.5:1, and a low corrected fan tip speedof less than 1150 ft/second.
 30. The turbine engine as recited in claim29, wherein the epicyclic gear train is intermediate a compressor rotorand a shaft driven by the fan drive turbine such that a fan rotor and afirst stage compressor are rotatable at a common speed.